Abstract: By using the pulsed laser single effect facility, the single event latch-up (SEL) effect experiments of two types of CMOS devices were studied. Based on the trigger mechanism of SEL effect in CMOS circuit, both two protection circuits of SEL effect and their hardness assurance mechanisms were discussed, as well as application scopes. The roles of two types of SEL mitigation circuits were verified with pulsed laser and heavy ions facilities. The results show that the current limiting resistance can effectively reduce the amplitude of the SEL current, but the circuit can not quit the state of the latch-up automatically, as the operation current of device is similar with latch-up holding current of device. The constant current source current-limiting mitigation circuit not only reduces the amplitude of the current SEL, but also quits the state of the latch-up automatically. It is a more effective mitigation technique of SEL effect in CMOS circuit.